The California Independent System Operator (CAISO) on April 30 said it has become one of the first wholesale power markets in the United States to connect a new and innovative battery storage technology to its grid. The four-year pilot project is intended to test and evaluate the performance of flow batteries in the commercial wholesale market. San Diego Gas & Electric, in coordination with Tokyo-based Sumitomo Electric, started testing a flow battery in 2015, according to CAISO, and the battery started participating in the ISO wholesale market in December.